Method for drawing fibers



W. R. SCHLEHR METHOD. FOR DRAWING FIBERS Nov, 16, 1948.

Filed March 20, 1946 M20 FIG.|

m v E NTO R WALTER R. SCHLEHR ATTORNEYS FIG. 2

- through small orifices.

latented Nov. 16 1 948 t 7: 1

METHOD FOR DRAWING FIBERS Walter R. Schlehr, Toledo, Ohio, assignor, by mesne assignments,. to Glass Fibers, Inc.,

Waterville, Ohio Application March 20, 1946, Serial No. 655,816

9 Claims. (01. 4977.5)

This invention relates to a method for drawing fine filaments from molten or semi-molten materials, and particularly directed to the drawing of fine filaments from molten glass. The invention is particularly directed to a process wherein the fine filaments are mechanically drawn from a supply or body of molten material, such as glass, and the filaments, as drawn, are wound upon a suitable reel or collected in any desired manner.

It has been found that semi-molten materials have a tendency to develop more satisfactory drawing characteristics when the material is worked at a temperature somewhat below the actual melting temperature of the material, but wherein the material is still in a highly viscous state so that it can be exuded through small orifices, This peculiar quality is particularly noticeable when drawing filaments from a body of molten glass. The major characteristic of the material that is improved is the tensile strength of the fibers or filaments which is increased substantially as the temperature at which the material is drawn is reduced.

However, as the drawing temperature of the material is reduced in an endeavor to obtain the higher tensile strength of the material, the molten material becomes more diiilcult to pass Therefore, to overcome the difiiculty of mechanically drawing the fibers or filaments from the body of molten material, such as glass, it has been proposed to utilize pressure upon the body of the glass of a sufiicient degree to cause the material to exude through small orifices at a lower working temperature. Such a method is disclosed in the copending application of Everett J. Cook, Serial No. 628,056 that is asigned to the same assignee as this instant patent application.

It is, therefore, an object of this invention to provide an improved method for drawing fine fibers or filaments of material mechanically wherein the pressure that is applied upon the body of the material to cause it to exude through small orifices is at least partially obtained from gases evolved from the body of material when the same passes from a solid to a molten condition.

It is still another object of the invention to provide an improved method in accordance with the foregoing object wherein the pressure of the gas upon the body of material is accurately controlled so that the material will be caused to exude through small orifices at a regular and constant rate.

It is still another object of the invention to provide an improved method for mechanically drawing fine fibers or filaments from a body of molten material wherein the gases that are evolved from the material are trapped above the body of the material and the pressure developed thereby is directly applied upon the body of material for causing the material to exude through small orifice openings.

It is still another object of the invention to provide an improved method in accordance with the foregoing object wherein the pressure applied upon the body of material is automatically controlled at a relatively constant value, and also wherein an auxiliary source of gas under pressure can supplement the pressure of the gas developed by that evolved from the body of material in transforming from the solid to the molten condition.

Further objects and advantages will become apparent from the drawings and the following description.

In the drawings:

Figure 1 is a cross-sectional view of an apparatus, shown somewhat schematically, for carrying forward. the methodof drawing fibers of this invention and of an apparatus for the same.

Figure 2 is a schematic electrical wiring diagram of a rectifier and oscillator for applying high frequency current upon the crucible in which the material is heated and rendered into a molten condition.

In Figure 1 there is illustrated an apparatus wherein a material can be heated to render it into a molten condition, and wherein gaseous pressure can be confined for application upon the body of molten material therein to cause the material to exude through small orifices provided in the bottom wall of the heating device.

- To obtain the gaseous pressure confined within the heating chamber for application upon the body of molten material therein, two sources oi gas are provided. One of the sources is from the body of material that is of a composition that a gas is evolved therefrom when it passes from a solid to a molten condition, and the second source of pressure may be an external source for aiding or supplementing the first source of pressure;

The subject matter of this invention will be particularly described with reference to the manufacture of glass fibers or filaments from a body of molten glass, but it will be understood that the principles of the invention disclosed herein are applicable to the production of fibers or filaments from materials other than glass including the ferrous or non-ferrous metals or alloys.

In the apparatus illustrated in Figure 1 there is provided a heating crucible I0 having a bottom wall ll provided with a plurality of small openings l2 therein. The heating crucible H1 is adapted to contain a body of molten material l3, such as glass.

A high .frequency induction coil I4 may be disposed around the lower end of the heating crucible l for the purpose of heating the crucible and thereby melting the glass therein. The heating crucible I0 is preferably constructed of platinum or a platinum alloy to withstand the temperature at which the glass is melted and the erosive action of the glass. The high frequency induction coil M is adapted to be connected to a source of high frequency energy, such as that illustrated in Figure 2, hereinafter described.

The heating crucible I0 is provided with an opening H5 in the top wall thereof. A pair of metal discs I6 and H are positioned in parallel relationship and are carried upon a shaft l8 suitably journaled within a bearing boss I9 secured to the feed hopper 20.

The metal discs I6 and I! pass over the opening H5 in the heating crucible I!) to control the feeding of pellets 25 of glass-making materials into the crucible l0 and to seal off the interior of the crucible ID from the atmosphere.

The lower disc Il may be provided with an opening 22 therein and a corresponding opening 23 may be provided in the upper disc I6, the opening 23 being displaced 130 from the opening 22. The spaced parallel relationship of the discs It and I1 provides a chamber 24 within the mouth 25 of the hopper 20 to allow the pellets 2| of glass-making materials to be received therein when the opening 23 is disposed within the mouth 25 of the hopper.

The rotation of the discs 16 and I1 concurrently will cause the opening 23 to seal off the chamber 24 from the hopper 20 so that when the opening 22 aligns with the opening E5 of the heating crucible iii, the pellets contained within the chamber 24 may pass through the opening 22 into the heating crucible l0 without allowing any substantial discharge of gas from within the heating crucible.

The discs 16 and I! carried upon the shaft l8 are rotated by means of an electric motor 26 driving the shaft l8 through a worm 21 and a worm wheel 28.

The heating crucible i0 is provided with a pres-- sure relief valve 30 for allowing exhaust of pressure above a predetermined value from within the interior of the crucible 10. The relief valve 30 is provided with a valve member 3| retained normally in closed position upon the valve seat of the inlet opening 32 by means of a spring 33 that is adjustable by means of the adjusting screw 34 to set the pressure at which the valve member will open to allow passage of gas through the conduit 35 for exhaust through the exhaust pipe 36. The conduit 35 communicates with the interior of the heating crucible Ill above the level of the body E3 of molten material therein.

There are four principal factors which govern the diameter of a fiber or filament during drawing thereof, and which factors can be correlated to obtain a desired filament diameter. After correlation of the factors they must remain constant during the drawing of the filament to maintain the diameter of the filament constant. These four main factors are (1) establishing a. predetermined temperature of the molten material, in this instance glass, from which the fibers are drawn and maintaining the temperature constant, (2) establishing a pressure upon the body of molten material, or a pressure differential upon opposite sides of the body of molten material, correlated with the temperature of the material to exude it through the openings in the wall of the heating crucible at a predetermined rate and to maintain the pressure constant during the drawing operation, (3) establishing a rate of drawing the fibers from the molten material at the discharge ends of the openings in the heating crucible that is correlated with the temperature of the material to mechanically draw the fibers to a predetermined degree of fineness as established by the rate of drawing and holding the rate of drawing constant during the drawing operation, and (4) establishing a predetermined size orifice in the wall of the heating crucible through which the material is exuded that is correlated to the temperature of the molten glass or material in the crucible and the pressure differential established upon the body of material to allow passage of the molten material through the orifice at a rate to allow drawing of the fibers from the molten material as it exudes through the orifice and yet retain a reservoir of molten material at the discharge side of the orifices from which the fibers can be drawn.

It has been found that to obtain a filament diameter of .00025", when manufacturing glass filaments, the most favorable conditions are to hold the temperature of the molten glass in the crucible It) at 2250 F. plus or minus 10 F. with the size of the orifices l2 at .040 plus or minus .006. The pressure maintained upon the body of the glass in the heating crucible I0 is equal to 10 of water in a water column gauge plus or minus 5" of water with a rate of draw of the filaments at approximately 10,000 feet per minute. The above conditions will maintain filament diameters of the desired size plus or minus .00002".

To obtain the desired pressure of approximately 10 of water upon the body I3 of molten glass, the materials that go into the composition of the glass may be such that the melting of the materials causes gas to evolve or be liberated therefrom. The choice of the gas that will be evolved or liberated must be made considering the composition of the glass and its relative solubility for various gases. In drawing glass fibers it is preferable that the glass shall be substantially seedfree, hence the volume of gas that can be dissolved by the molten glass shall be relatively small. Thus, when using any ordinary soda-lime glass, oxygen and nitrogen would be preferable gases to use as the atmosphere within the heating crucible because they are relatively insoluble in the molten glass. In a boro-silicate glass, particularly where little or no alkali oxides are present, carbon dioxide is comparatively insoluble. Therefore, in developing a furnace atmosphere and a pressure within the heating crucible 10 by the gas liberated from the composition, the nature of the constituents of the glass will Vary depending. upon the gas that is to be liberated.

As for example, a batch composition for glass that would satisfactorily evolve or liberate sufilcient quantities of carbon dioxide gas to develop pressure within the heating crucible ID may consist of Per cent parts by weight Raw dolomite CaMg(CO3)z 22.4 Raw limestone CaCO; 17.4 Calcined borax NazBiov 5% Boric acid HsBOs 5 Kyanite (A10)2Si03 23%. Sand SiOz 48 A;

The above materials may be pressed into the forms of pellets, after mixing of the materials, and introduced into the hopper 20 of the apparatus.

When the pellets 2| are melted within the crucible l9, carbon dioxide gas will be liberated to produce pressure within the furnace or heating crucible Ill.

The pressure relief valve 30 is suitably adjusted to allow excess carbon dioxide gas to exhaust from the interior of the crucible l should the pressure rise above the desired value, such as 10" of water as hereinbefore set forth.

To supplement, or augment, the pressure developed by the gas liberated from the molten material within the crucible l0, should insufficient gas be liberated, an auxiliary pressure supply 40 may be provided. The gas preferably would be the same as that evolved from the body of molten material. However, other gases could be used so long as they did not dissolve readily in the molten material. The source of gas under pressure 40' may be connected with the interior of the furnace or heating crucible I!) by means of a conduit 4| in which there is placed a pressure control valve 42.

As long as the pressure within the crucible I0 is at the value for which the valve 30 is set, thus indicating that sufficient gas is liberated from the materials melting within the furnace, the valve 42 will not allow gas from the auxiliary source 40 to enter the interior of the crucible |ll. However, should insufficient gas be liberated from the glass materials melting within the furnace II], the valve 42 willopen to allow pressure from the source 40 to be delivered through the conduit 4| into the interior of the crucible Ill.

The valve 42 consists of a spring-pressed plunger 43 having the heads 44 and 45 thereon. The head 45 controls the inlet port 46 so that when pressure in the conduit 4| is sumciently high and engages the lower face of the head 45 through the control passage 47, the port 46 will be closed. However, when the pressure within the pipe 4| reduces, the spring 48 will force the head 45 downwardly to open the port 46 in proportion to the drop in pressure until the pressure in the pipe 4| has been restored to its normal value. The spring 48 is adjustable by the adjustment member 49 so that the valve 42 can be adjusted to cooperate with the Valve 30.

The pressure within the heating crucible l0 may thus be maintained at a constant level with the gas liberated from the melting materials being used as the primary source of pressure and the external source of pressure as an auxiliary or augmenting source of pressure.

In Figure 2 there is illustrated a schematic wiring diagram for operating the apparatus illustrated in Figure 1. In general, the electrical system consists of a full wave rectifier 60 having the output thereof connected with an oscillator unit '10. The oscillator 10 may consist of an oscillator tube II that connects with the transformer 12 which in turn is connected to the high frequency coil l4.

The output of the oscillator may be controlled by varying the voltage in the grid circuit of the oscillator tube 1| by means of a variable resistor 13 which is operated in one direction to decrease the output of the oscillator by means of a motor 14, and is operated in the opposite direction by means of a torsion spring or motor 15 that is connected to the common shaft of the motor 14 to increase the output of the oscillator 10. The spring motor 15 is normally active to increase the output of the oscillator 10 except when the motor 14 is energized in response to a thermal control 6. element 16 which'is sensitive to the temperature of the heatingcrucible ID.

A relay coil A is connected in series with the temperature-sensitive device 16 so that when circuit is made through the relay coil A indicating a high temperature of the crucible ID, or temperature satisfaction thereof, the contacts A1 will be closed to energize the motor 14 and thereby reduce the output of the oscillator 10. When circuit is broken through the relay A the contacts A1 will open to de-energize the motor 14 and allow the spring motor 15 to operate the resistance member 13 to increase the output of the oscillator Ill. Constant temperature control of the crucible I0 is thereby obtained.

The motor 26 for feeding pellets of material to be melted is operated in response to the level of the body of material |3 within the crucible ID. A contactor 8D is placed in circuit with a relay coil C, an electric circuit being adapted to be completed through the contactor 80, the body of molten glass I3 and the crucible l0 for making or breaking circuit through the relay coil C.

When the level of molten glass is such as to engage the bottom of the contactor 80, electric circuit is completed through the relay C to open the relay contactor C1 thereby stopping operation of the motor 26, and halting the feeding of pellets into the crucible in. However, when the body of molten glass falls below the end of the contactor 80, electric circuit will be broken through the relay C to allow the contactor C1 to close and thereby energize the motor 26 for again feeding pellets of material into the crucible The feeding of the pellets 2| into the crucible ID will thus replenish the supply of material as used therefrom and will provide for replenishment of gas that may escape from the furnace or crucible.

While the method and apparatus disclosed herein constitute a preferred form of the invention, yet it will be understood that the apparatus and the method of operating the same is capable of alteration without departing from the spirit of the invention, and that all modifications that fall within the scope of the appended claims are intended to be included herein.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent is:

1. The method of producing fibers or filaments which includes, feeding glass stock capable of evolving a gas having a low solubility in molten glass into a heating chamber having a plurality of apertures in one wall thereof, heating the glass stock within the chamber to melt the same with consequent liberation of gas therefrom to control the atmosphere in the chamber thereby and render the glass free of seeds, retaining at least a portion of the liberated gas within the heating chamber to establish a pressure above atmosphere upon the body of material therein to exude the melted material through the apertures, and attenuating the material as exuded into fine fibers.

2. The method of producing fibers or filaments that includes, introducing glass-making materials capable of liberating a gas having a low solubility in molten glass into a heating chamber having a plurality of apertures in one wall thereof, melting the materials in the chamber with consequent liberation of gas therefrom to control the atmosphere in the chamber thereby and render the glass free of seeds, retaining the liber- "atedg'as within the chamber "to establish a pressure above atmosphere Within the chamber to exude the melted material from the chamber through said apertures, and attenuating the material exuded into fine fibers.

3. The method of producing fibers or filaments which includes, feeding glass stock capable of evolving a gas having .a low solubility inmolten glass into a heating chamber having a plurality of apertures in one Wall thereof, heating the glass :render the glass free of seeds, retaining at least a portion of the liberated'gas within the heating chamber to establish and maintain a predetermined pressure above atmosphere upon the body of material therein to exude the melted material through the apertures, and attenuating the material as exuded into fine fibers.

4. The method of producing fibers or filaments which includes, feeding material capable of evolving a gas having low solubility in the material into a heating chamber having a plurality of apertures in one wall thereof, heating the ma terial within the chamber to melt the same with consequent liberation of gas therefrom to control the atmosphere in the chamber thereby and render the material free of gas bubbles, retaining 'at least a portion of the liberated gas within the heating chamber to establish a pressure above atmosphere upon the body of material therein to exude the melted material through the -apertures, and attenuating the material as exuded into fine fibers.

5. The method of producing fibers or filaments which includes, feeding material capable of evolving a gas having low solubility in the material into a heating chamber having a plurality of apertures in one wall thereof, heating the material Within the chamber to melt the same with consequent liberation of gas therefrom to control the atmosphere in the chamber thereby and render the material free of gas bubbles, retaining at least a portion of the liberated gas within the heating chamber to establish and maintain a predetermined pressure above atmosphere upon the body of material therein to exude the melted material through the apertures, and attenuating the material as exuded into fine fibers.

6. The method of producing fibers or filaments that includes, introducing materials from which the fibers or filaments are produced into a heating chamber having a plurality of orifices in one Wall thereof, which materials are capable of libcrating gas having low solubility in the molten material upon heating thereof, heating the materials within the heating chamber to render them viscous with consequent liberation of gas therefrom to control the atmosphere in the chamber thereby and render the material free of gas bubbles, confining the liberated gas within the heating chamber to establish and maintain a gas pressure above atmosphere upon the body of viscous material therein to exude the material through the orifices, and attenuating the viscous material into fibers as exuded from the orifices.

7. The method of producing fibers or filaments that includes, introducing materials from which the fibers or filaments are produced into a'heating chamber having a plurality of orifices in one wall thereof, which materials are capable of libcrating gas hailing low solubility in the molten material upon heating thereof, heating the materials within the heating chamber to render them viscous with consequent liberation of gas therefrom to control the atmosphere in the chamber thereby and render the material free of bubbles, confinin the liberated gas within the heating chamber to establish and maintain a gas pres'sure above atmosphere upon the body of viscous material therein to exude the material through the orifices, exhausting a part of the liberated gases from the heating chamber in response to the pressure in the heating chamber to maintain the pressure therein constant, and attenuating the viscous material into fibers as exuded from the orifices.

3. The method'of producing fibers or filaments that includes, introducing materials from which the fibers or filaments are produced into a heat- 2mg chamber having a plurality of orifices in one wall thereof, which materials are capable of liberating gas having 'low solubility in the molten material upon heating thereof, heating the materials within the heating chamber to render them viscous with consequent liberation of gas therefrom to control the atmosphere in the ehamberthereby and render the material free of gas bubbles, confining the liberated gas Within the heating chamber to establish and maintain a gas pressure above atmosphere upon the body of viscous material therein to exude the material through theorifices, introducing a like gas into the heating chamber from an external source of supply to augment the supply of gases liberated within the heating-chamber, and attenuating the viscous material into fibers as exuded from the orifices.

'9. The method of producing fibers or filaments that includes, introducing materials from which the fibers or filaments are produced into a heat ing chamber having a plurality of orifices in one "wall thereof, which materials are capable of libcrating gas having low solubility in the molten material 'uponheating thereof, heating the ma- T ter'ials within the heating chamber to render them viscous with consequent liberation of gas therefrom to control the atmosphere in the chamber thereby and render the material free of gas bubbles, confining the liberated gas Within the heating chamber to establish and maintain a gas pressure above atmosphere upon the body of viscous material therein 'to exude the material through the orifices, exhausting a part of the liberated gases from the heating chamber to maintain the pressure therein constant, introducing a like gas into the heating chamber from an external source of supply to augment the supply of gases liberated within the heating chamber, and attenuating the viscous material into fibers as exuded from the orifices.

WALTER R. SCl-ILEHR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,159,361 Atkinson et a1. May 23, 1939 2,229,489 Barnard Jan. 21, 1941 2,294,266. Barnard Aug, 25, 1942 

